Fixes build with Python >= 3.6:

------
Making all in libgnomeui
make[2]: Entering directory '/tmp/guix-build-libgnomeui-2.24.5.drv-0/libgnomeui-2.24.5/libgnomeui'
  GEN    stamp-gnome-marshal.h
  GEN    stamp-gnometypebuiltins.h
INFO: Reading ./gnome-marshal.list...
  GEN    gnome-marshal.h
Traceback (most recent call last):
  File "/gnu/store/...-glib-2.54.2-bin/bin/glib-mkenums", line 688, in <module>
    process_file(fname)
  File "/gnu/store/...-glib-2.54.2-bin/bin/glib-mkenums", line 420, in process_file
    line = curfile.readline()
  File "/gnu/store/...-python-3.6.3/lib/python3.6/codecs.py", line 321, in decode
    (result, consumed) = self._buffer_decode(data, self.errors, final)
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xf1 in position 1009: invalid continuation byte
make[2]: *** [Makefile:1109: stamp-gnometypebuiltins.h] Error 1
make[2]: Leaving directory '/tmp/guix-build-libgnomeui-2.24.5.drv-0/libgnomeui-2.24.5/libgnomeui'
make[1]: *** [Makefile:369: all-recursive] Error 1
make[1]: Leaving directory '/tmp/guix-build-libgnomeui-2.24.5.drv-0/libgnomeui-2.24.5'
make: *** [Makefile:296: all] Error 2
------

Patch copied from upstream source repository:

https://git.gnome.org/browse/libgnomeui/commit/?id=30334c28794ef85d8973f4ed0779b5ceed6594f2

From 30334c28794ef85d8973f4ed0779b5ceed6594f2 Mon Sep 17 00:00:00 2001
From: Colin Walters <walters@verbum.org>
Date: Mon, 7 Aug 2017 13:15:26 -0400
Subject: [PATCH] gnome-scores.h: Convert to UTF-8

The new Python `glib-mkenums` barfs on ISO-8859-1 input.
---
 libgnomeui/gnome-scores.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libgnomeui/gnome-scores.h b/libgnomeui/gnome-scores.h
index 911b12d1..4e641d22 100644
--- a/libgnomeui/gnome-scores.h
+++ b/libgnomeui/gnome-scores.h
@@ -27,7 +27,7 @@
  * "High Scores" Widget 
  *
  * AUTHOR: 
- * Horacio J. Peña <horape@compendium.com.ar>
+ * Horacio J. Peña <horape@compendium.com.ar>
  *
  * This is free software (under the terms of the GNU LGPL)
  *
c11f8a8800350ef53a5'>root</a>/<a href='/guix/log/nix?id=157b94ead7ea64c945b8dc11f8a8800350ef53a5'>nix</a>/<a href='/guix/log/nix/libutil?id=157b94ead7ea64c945b8dc11f8a8800350ef53a5'>libutil</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/nix/libutil?id=157b94ead7ea64c945b8dc11f8a8800350ef53a5&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2023-01-09 17:40:54 +0100'>2023-01-09</span></td><td><a href='/guix/commit/nix/libutil?id=407175a1d0e29f45639e7f28a531b3981cd20085'>daemon: Improve error message for wrong hash sizes.</a><span class='msg-avail'>...<span class='msg-tooltip'>* nix/libutil/hash.cc (parseHash): Show the hash algorithm name and
expected size in the error message.
* tests/derivations.scm ("fixed-output derivation, invalid hash size"):
New test.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2022-12-18 01:16:47 +0100'>2022-12-18</span></td><td><a href='/guix/commit/nix/libutil?id=2d4d26769d6a3be1b21302b0bb2bd099fd55ccf8'>daemon: Make "opening file" error messages distinguishable.</a><span class='msg-avail'>...<span class='msg-tooltip'>* nix/libstore/build.cc (DerivationGoal::openLogFile): Customize
"opening file" error message.
* nix/libutil/hash.cc (hashFile): Likewise.
* nix/libutil/util.cc (readFile, writeFile): Likewise.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-11-19 23:04:19 +0100'>2021-11-19</span></td><td><a href='/guix/commit/nix/libutil?id=24224530d1f4a70808d003ba8dce849b77625b79'>daemon: Micro-optimize 'deletePath'.</a><span class='msg-avail'>...<span class='msg-tooltip'>'remove' calls 'unlink' first and falls back to 'rmdir' upon EISDIR.
This change gets rid of the 'unlink' call for every directory being
removed.

* nix/libutil/util.cc (_deletePath): Call 'unlink' or 'rmdir' depending
on 'st.st_mode', rather than call 'remove'.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-12-08 22:30:07 +0100'>2020-12-08</span></td><td><a href='/guix/commit/nix/libutil?id=2e308238ad09e9527f9b8c3ec4a90b6b05a93367'>daemon: 'Agent' constructor takes a list of environment variables.</a><span class='msg-avail'>...<span class='msg-tooltip'>* nix/libutil/util.hh (struct Agent)[Agent]: Add 'env' parameter.
* nix/libutil/util.cc (Agent::Agent): Honor it.
</span></span></td><td>Ludovic Courtès</td></tr>